MCAT CHAPTER 1

Cell Theory

The scientific theory stating that all living things are composed of cells, the cell is the basic unit of life, and all cells come from pre-existing cells.

Tenets of Cell Theory

All living organisms are made of one or more cells.The cell is the basic unit of structure and function in living things. All cells arise only from pre-existing cells. Cells contain hereditary information DNA and pass it on during cell division.

Modern Cell Theory Additions

Cell contain hereditary information DNA that is passed to daughter cells. All energy flow (metabolism) occurs within cells.

Basic Unit of Life

The smallest structure capable of performing all life processes. The cell

Spontaneous Generation

The disproven idea that living organisms can arise from nonliving matter.

Louis Pasteur

Scientist who disproved spontaneous generation with swan-neck flask experiment, supporting that all cells come from pre-existing cells

Robert Hooke

First to use the term “cell” after observing cork under a microscope in 1665

Matthias Schleiden

Botanist who proposed that all plants are made of cells

Theodore Schwann

Zoologist who concluded that all animals are made of cells

Rudolf Virchow

Proposed that all cells arise from pre-existing cells

Prokaryotic Cell

A simple cell without a nucleus or membrane-bound organelles(e.g., bacteria)

Eukaryotic Cell

A complex cell containing a nucleus and membrane-bound organelles (e.g., plant and animal cells)

Unicellular Organism

A single-celled organism that performs all life functions within one cell

Multicellular organism

An organism composed of many specialized cells working together

Cell Membrane (plasma membrane)

A selective barrier that controls what enters and leaves the cell

Cytoplasm

the fluid region of the cell where organelles are suspended and reactions occur

Nucleus

Organelle that stores genetic information (DNA) in eukaryotic cells

DNA (Deoxyribonucleic Acid)

The hereditary material that contains genetic instructions passed to daughter cells

Mitochondria

Organelles that produce ATP and contain their own DNA, suggesting an endosymbiotic origin

Chloroplast

Photosynthetic organelle in plants that also contains its own DNA

Endosymbiotic Theory

The theory that mitochondria and chloroplasts evolved from free-living prokaryotes engulfed by larger cells

Virus

A non-cellular infectious agent that require a host cell to replicate. Not considered alive under cell theory

Prion

An infectious protein lacking nucleic acids and cellular structure; violates cell theory

Platelet

A cell fragment in blood that lacks a nucleus. An exception to typical cell structure

Red Blood Cell (Erythrocyte)

A mammalian cell that loses its nucleus to carry oxygen efficiently; still a product of a pre-existing cell

Cell Divistion

The process by which a patient cell divides to from new daughter cells (mitosis or meiosis)

Binary Fission

The process of cell division in prokaryotes where one cell splits into two

Stem Cell

An undifferentiated cell capable of giving rise to specialized cells, supporting the idea that cells come from pre-existing ones

Metabolism

All chemical reactions that occur within cells to maintain life

Cell Differentiation

the process by which unspecialized cells become specialized in structure and function

Cytology

The scientific study of cells, their structure, and function

Microscope

Instrument used to magnify and observe cells, essential for cell theory discovery

Cell lineage

The tracing of a cell’s ancestry back to parent cell. Supports the third tenet of cell theory

Abiogenesis

The natural process by which life originally arose from nonliving matter (Earth), distinct from spontaneous generation

Tissue

A group of similar cells that perform a specific function

Organ

A structure made of different tissues working together for a common function

Organ System

A group of organs that perform coordinated function in a multicellular organism

Organelle

Specialized structure within a cell that performs a specific function (e.g., mitochondria, ribosomes.)

Cytoskeleton

A network of protein filaments ( microfilaments, intermediate filaments, microtubules) that provides structure, transport, and movement within the cell

Microfilaments (Actin Filaments)

Thin protein fibers made of actin; involved in cell movement, shape, and division (Cytokinesis)

Intermediate Filaments

Cytoskeleton components that provide mechanical strength and maintain cell shape

Microtubules

Hollow tubes made of tubulin; important for cell shape, intracellular transport, and mitotic spindle formation

Centrioles

Cylindrical organelles near the nucleus that help organize microtubules during cell division

Spindle Apparatus

Structure of microtubules that separates chromosomes during mitosis and meiosis

Mitosis

Cell division process producing two genetically identical diploid daughter cells

Meiosis

Cell division producing four genetically distinct haploid gametes (sex cells)

Cell Cycle

The ordered series of events in cell growth and division: G1, S, G2 and M phases

G1 Phase

First growth phase where the cell increases in size and synthesizes proteins

S

DNA replication phase of the cell cycle

G2 Phase

Second growth phase where the cell prepares for mitosis by producing organelles and proteins

M Phase

mitotic phase where cell division occurs (mitosis+Cytokinesis)

G0 Phase

Resting or non-dividing state of a cell, often for differentiated cells

Checkpoints (cell cycle)

Control mechanisms (G1/S, G2/M, spindle) that ensure proper DNA replication and division

Apoptosis

Programmed cell death that removes damaged or unnecessary cells

Necrosis

Uncontrolled cell death due to injury or lack of oxygen

Cancer

Disease caused by uncontrolled cell division due to loss of cell cycle regulation

Oncogene

A mutated or overactive gene that promotes cell division and can lead to cancer

Tumor Suppressor Gene

Gene that prevents uncontrolled cell division; loss of its function can cause cancer (e.g., p53)

P53 Protein

A tumor suppressor that halts the cell cycle for DNA repair or triggers apoptosis if damage is severe

Chromatin

DNA and associated proteins (histones) in the nucleus; condenses into chromosomes during cell division

Chromosome

Thread-like structure made of DNA and proteins that carries genetic information

Chromatid

One of two identical halves of a replicated chromosome

Centromere

the region where sister chromatids are joined and where spindle fibers attach during division

Kinetochore

Protein complex on the centromere where spindle fibers bind

Cytokinesis

Division of the cytoplasm following mitosis or meiosis to form two cells

Endoplasmic Reticulum (ER)

Network of membranes involved in protein and lipid synthesis

Rough ER

ER with ribosomes attached; site of protein synthesis and folding

Smooth ER

ER without ribosomes; synthesizes lipids, detoxifies drugs, and stores calcium

Golgi Apparatus

Modifies, sorts, and packages proteins and lipids for secretion or transport

Lysosome

Organelle containing digestive enzymes that break down waste and cellular debris

Peroxisome

Organelle that breaks down fatty acids and detoxifies harmful substances

Ribosome

Cellular structure that synthesizes proteins using mRNA templates; found i cytoplasm or on rough ER

Nucleolus

Dense region inside the nucleus where ribosomal RNA (rRNA) is synthesized

Nuclear Envelope

Double membrane surrounding the nucleus with pores for molecule exchange

Nuclear Pore

Opening in the nuclear envelope allowing transport of RNA and proteins

Mitochondrial DNA (mtDNA)

Circular DNA found in mitochondria; inherited maternally and codes for some mitochondrial proteins

ATP (Adenosine Triphosphate)

The primary energy currency of the cell

Cell Junctions

Structures that connect cells together and facilitate communication

Tight junction

Seals cells together to prevent leakage (e.g., in intestinal lining)

Desmosome

Anchoring junction providing mechanical strength between cells

Gap junction

Channel allowing ions and small molecules to pass between cells for communication

Cell signaling

Process by which cells communicate through chemical signals (ligands and receptors)

Ligand

Molecule that binds to a receptor to trigger a response (e.g., hormone, neurotransmitter)

Receptor

Protein that receives and responds to chemical signals on or inside a cell

Signal transduction pathway

Series of molecular events converting an extracellular signal into a cellular response

Second Messenger

Small molecule that transmits a signal from a receptor to a target (e.g., cAMP, Ca2+)

Endocytosis

Process by which a cell takes in material by engulfing it in a vesicle

Exocytosis

Process by which materials are expelled from the cell through vesicle fusion with the plasma membrane

Phagocytosis

Cell eating. Engulfing large particles or other cells

Pinocytosis

Cell drinking. Intake of extracellular fluid and small molecules

Receptor-Mediated Endocytosis

Specific uptake of substances via receptor binding and vesicle formation

Osmosis

Diffusion of water across a semipermeable membrane from low to high solute concentration

Diffusion

Movement of molecules from an area of thigh concentration to low concentration

Facilitated Diffusion

Passive transport using protein channels or carriers

Active Transport

Movement of molecules against their concentration gradient using energy (ATP)

Sodium-Potassium Pump (Na+/K+-ATPase

Active transport protein that maintains electrochemical gradients by pumping Na+ out and K+ in

Endomembrane System

Network of membranes including the ER, Golgi, lysosomes, vesicles, and plasma membrane

Vesicle

Small membrane sac that transports materials within or between cells

Extracellular Matrix (ECM)

Network of proteins and carbohydrates outside animal cells that provides support and communication

Cell Wall

Rigid outer layer found in plants, fungi, and bacteria; provides structural support and protection